Systems and methods for reducing dead volume in compressed-gas energy storage systems

Abstract

In various embodiments, dead space and associated coupling losses are reduced in energy storage and recovery systems employing compressed air via use of a compressed-gas reservoir for maintaining a connector between cylinder assemblies at an intermediate pressure, thereby reducing the volume of dead space in the connector and increasing efficiency of the energy storage and recovery.

1. An energy storage and recovery system comprising:
 a first cylinder assembly, comprising first and second separated compartments, for, over a first range of pressures, at least one of (i) compression of gas to store energy or (ii) expansion of gas to recover energy; 
 a second cylinder assembly, comprising first and second separated compartments, for at least one of compression or expansion of gas over a second range of pressures (i) different from the first range of pressures and (ii) overlapping the first range at an intermediate pressure; 
 a connector selectively fluidly connecting the first compartments of the first and second cylinder assemblies; and 
 a compressed-gas reservoir, fluidly connected to the connector, for maintaining the connector at the intermediate pressure, thereby reducing a volume of dead space in the connector and increasing efficiency of the energy storage and recovery. 
 
     
     
       2. The system of  claim 1 , wherein the first and second cylinder assemblies are coupled in series pneumatically. 
     
     
       3. The system of  claim 1 , wherein the reservoir has a volume sufficient to supply gas to an entire volume of the connector while maintaining a substantially constant pressure within the reservoir. 
     
     
       4. The system of  claim 1 , wherein the reservoir has a volume sufficient to supply gas to an entire volume of the first compartment of at least one of the first or second cylinder assemblies while maintaining a substantially constant pressure within the reservoir. 
     
     
       5. The system of  claim 1 , wherein the reservoir comprises a pressure-compensated vessel. 
     
     
       6. The system of  claim 1 , wherein the first and second cylinder assemblies each comprise a movable boundary mechanism separating the first and second compartments. 
     
     
       7. The system of  claim 6 , further comprising a crankshaft coupled to each of the movable boundary mechanisms via a throw. 
     
     
       8. The system of  claim 7 , wherein an angle between the throws is substantially different from 180°. 
     
     
       9. The system of  claim 1 , further comprising a heat-transfer system for introducing, within at least one of the compartments of at least one of the first or second cylinder assemblies, heat-transfer fluid for exchanging heat with gas, thereby increasing efficiency of the energy storage and recovery. 
     
     
       10. The system of  claim 9 , wherein the heat-transfer system comprises at least one of a spray head or a spray rod. 
     
     
       11. The system of  claim 9 , further comprising a heat exchanger and a circulation apparatus for circulating the heat-transfer fluid between the heat exchanger and the at least one cylinder assembly. 
     
     
       12. The system of  claim 1 , wherein at least one of the first or second cylinder assemblies comprises a pneumatic cylinder. 
     
     
       13. The system of  claim 1 , wherein at least one of the first or second cylinder assemblies comprises a pneumatic/hydraulic cylinder. 
     
     
       14. The system of  claim 1 , further comprising, selectively fluidly connected to at least one of the first or second cylinder assemblies, (i) a second compressed-gas reservoir, different from the compressed-gas reservoir, for storage of gas after compression and supply of compressed gas for expansion thereof, and (ii) a vent for exhausting expanded gas to atmosphere and supply of gas for compression thereof. 
     
     
       15. The system of  claim 1 , further comprising, connected to at least one of the first or second cylinder assemblies, an intermittent renewable energy source of wind or solar energy, wherein (i) energy stored during compression of the gas originates from the intermittent renewable energy source, and (ii) energy is recovered via expansion of the gas when the intermittent renewable energy source is nonfunctional. 
     
     
       16. An energy storage and recovery system comprising:
 a plurality of independently operative cylinder groups for at least one of compression of gas to store energy or expansion of gas to recover energy, each cylinder group comprising (i) a plurality of cylinder assemblies, at least two of the cylinder assemblies being configured to operate over pressure ranges overlapping at an intermediate pressure, and (ii) a connector selectively fluidly connecting the cylinder assemblies; and 
 a compressed-gas reservoir, fluidly connected to each connector, for maintaining each connector at the intermediate pressure, thereby reducing a volume of dead space in each connector and increasing efficiency of the energy storage and recovery. 
 
     
     
       17. The system of  claim 16 , wherein the reservoir has a volume sufficient to supply gas to an entire volume of each connector while maintaining a substantially constant pressure within the reservoir. 
     
     
       18. The system of  claim 16 , wherein each cylinder group comprises:
 a first cylinder assembly, comprising first and second separated compartments, for at least one of compression or expansion of gas over a first range of pressures; and 
 a second cylinder assembly, comprising first and second separated compartments, for at least one of compression or expansion of gas over a second range of pressures (i) different from the first range of pressures and (ii) overlapping the first range at the intermediate pressure. 
 
     
     
       19. The system of  claim 18 , wherein the reservoir has a volume sufficient to supply gas, for each cylinder group, to an entire volume of the first compartment of at least one of the first or second cylinder assemblies while maintaining a substantially constant pressure within the reservoir.